Temperature monitoring, and therefore temperature measurement, during a charging process is a frequent requirement for battery charging devices. This is so that excessively high or excessively low temperatures can be avoided, which is a necessary condition for destruction-free charging for a number of battery types such as lithium-ion rechargeable batteries.
Methods for precise temperature measurement are often based on the use of semiconductor temperature sensors. Thermistors, especially NTC resistors, i.e., thermistors with negative temperature coefficients, are generally used and make it possible to measure the temperature as a function of a variable resistance. These switching elements are frequently already installed in batteries.
A disadvantage of using thermistors is the occurrence of large differences of resistance within the temperature limits that are critical for battery-charging processes, which temperature limits lie between 0° C. and 50° C. for lithium ion batteries. There is a difference of as much as 10 kΩ in the resistances of a thermistor within such an interval. Simple constant current circuits or resistive voltage dividers are therefore usually not suitable for a precise temperature measurement. One solution to this problem is to use several voltage comparators, connected as window comparators, for example, that correspond to the temperature interval for the measurement. Offset errors in the voltages that are present at the comparators and that are dependent on the charging current of the battery, as well as any loads attached, are a disadvantage of such an implementation. This consequently complicates an exact temperature measurement.